JPH02260688A - Superconductive thick film for hybrid circuit parts - Google Patents

Abstract

PURPOSE: To obtain a superconducting thick film as thick as 5μm or above for a circuit part by a method wherein a mixture of heavy pnictide oxides, alkaline earth oxides and copper oxides are formed on a substrate of aluminum oxide or aluminum nitride. CONSTITUTION: Composition which contains metal-ligand compound particles is obtained through a process A. The compound particles contain pnictide oxides, alkaline earth oxides and copper oxides at the same ratio that a final pnictide- mixed alkaline earth copper oxides (PAC)-containing conductive layer is required to have. A substrate 3 is coated with the compound particles together with carrier liquid in a process B, wherein the substrate 3 is formed of aluminum oxide or aluminum nitride. An obtained article 1 is composed of the substrate 3 and a layer 5 formed of PAC precursor. In processes C, D, E, and F, heating, pre-burning, burning, and after-burning are carried out for the formation of articles 7, 11, 15, and 19. A final electric conductive article 19 is formed of a crystalline electric conductive PAC layer 21 on the substrate 3 and as thick as 5μm or above to serve as a superconductive thin film used for a circuit part.

Description

[Detailed description of the invention] [Industrial application field] This invention relates to thick film electrical conductors.

[Conventional technology]

The term "superconductivity" applies to the phenomenon of immeasurably low electrical resistance exhibited by materials.

Until recently, superconductivity has been reproducibly demonstrated only at temperatures near absolute zero. When a material capable of exhibiting superconductivity is cooled, a temperature is reached at which the resistivity decreases significantly (conductivity increases) as a function of further decrease in temperature. This is called the transition temperature at which superconductivity begins, or simply the critical temperature (Tc) in the context of superconductivity research. Tc indicates the onset of superconductivity and provides a conveniently identified and commonly accepted reference point to give the temperature order of superconductivity in different materials. The maximum temperature at which superconductivity can be measured in a substance is called To.

Unless otherwise indicated, the term "thick film" means a film that has a thickness greater than 500 ml, while the term "thin film" in all instances is less than 500 ml, typically less than IJ
means a film having a thickness that is less than a.

T,) Iashimoto, T, Kosaka, Y
, Yoshida, K., Fueki.

and HoKoinuma, “5uppercondu
ctivity and 5ubstrateInte
action of 5clean-Printed
B1-3r-Ca-Cu-[1Fil+r+s”,
Japanese Journal of Appli
ed Physics.

Vol, 27. No, 3. March 1988, l1f)
, LaB5-LaB5 Nii-! , on a yttrium stabilized zirconia and strontium titanate substrate,
Successful attempts have been reported to form superconducting thick films of bismuth strontium calcium copper oxide.

Tlashimoto et al failed to make superconducting films on quartz and alumina substrates. This thick film was manufactured by screen printing.

Bismuth strontium calcium copper oxides with nominal compositions of 1112 and 2213 are prepared by calcining bismuth oxide and copper oxide with strontium carbonate and calcium carbonate at 800°C for 12 hours, and then adding milk with octyl alcohol. Manufactured by mixing with a pestle to form a paste. This paste was screen printed.

T, Nakamori, l(, Abe, Y, Tak
ahasi, T., Kanamort.

and S, 5hibata, “Preparatio
n of SuperconductlngBi-Ca
-3r-Cu-OPr1nted Th1ck Fil
ms Using a Coprecipitation
of Oxalates, Japanese J
our applied physics,
Vol, 27. No. 4. April 1983, pp.
L649-L651 report successful attempts to form superconducting thick films of bismuth strontium calcium copper oxide on single crystal magnesia substrates. This thick film was manufactured by screen printing. Calcium chloride, strontium chloride, and copper chloride were co-precipitated with oxalate. Bismuth oxalate was precipitated separately from acetone. These two precipitates were washed separately, filtered, dried and then mixed as a solid,
It is then heated to 300° C. to produce bismuth strontium calcium copper oxide having a nominal composition of 1112.

K, Ho5hino, H, Takahara, and M, Fukutom+.

”Preparation of Supercond
ucting B1-3r-Ca-Cu-OPr1nt
ed Th1ck Films on MgO5ubs
treat and Ag Metal Tape,
Japanese Journal of AppHe
dPhysics, Vol, 27. No, 7.19
July 1988, pp. L1297-L1299 describes bismuth strontium calcium on a single crystal magnesia substrate, silver, and some metal tapes,
It was manufactured by a power firing technique similar to that described by moto et al. This bismuth strontium calcium copper oxide had a nominal composition of 1112.

It is clear that between thick and thin films of superconducting ceramic oxide, higher currents in superconducting mode are supported by the former. In an attempt to produce thick films of depnictide mixed alkaline earth copper oxides, the most homogeneous and intimate mixture of precursors forming mixed metal oxides was used to avoid the local formation of mixed low conductivity facies. It is desirable to achieve the potential.

Uniform and intimate mixing of the precursors is achieved by placing the salts of the metals in the desired proportions into a solution, coating the solution onto the substrate, and then producing thin films of bismuth mixed alkaline earth copper oxides.
and achieved by removing the solvent. It is then heated to form the desired crystalline mixed metal oxide. Although this approach works well for producing thin films with a thickness (thickness typically measured in angstroms) well below 1-1, it is not viable for forming thick films. It's not an approach.

The final coating thickness is much smaller than the thickness of the solution layer containing the precursor. Attempts to increase the thickness of the solution layer, such as by increasing its viscosity, have shown that the high thickness shrinkage of the solution coating upon heating creates a thick film that is full of pores with stress cracks; , is not viable as a poor electrical conductor is formed.

Hashimoto et al, Nakamori
et al and Ho5hin.

et al all seek to form intimate mixtures of bismuth mixed alkaline earth copper oxides by physically mixing the solids (eg, calcining the mixed solids). The difficulty with this approach is that intimate, homogeneous mixtures of the precursors, which can be obtained by placing the precursors in common solvents, cannot be achieved by repeated and laborious blending.

A further problem remains that thick films of superconducting bismuth alkaline earth copper mixed oxides have never been coated onto substrates made of oxides or nitrides of aluminum.

[Problem to be solved by the invention]

It is an object of the present invention to provide a superconducting thick film coating of heavy pnictide alkaline earth copper mixed oxides on a substrate consisting of aluminum oxide or aluminum nitride.

[Means to solve the problem]

In one aspect, the present invention provides a circuit element comprising (i> superconducting crystalline pnictide alkaline earth copper mixed oxide and (ii) a substrate, wherein the substrate is aluminum oxide or aluminum nitride. It relates to circuit elements that perform

The present invention is generally applicable to all known electrically conductive heavy pnictide mixed alkaline earth copper oxide compositions. Term rPA
CJ is generally used herein as an acronym for heavy pnictide mixed alkaline earth copper oxide.

The acronym 3g rRAc J is used to indicate the rare earth alkaline earth copper oxide composition and is sometimes referenced to compare and contrast the properties of the PAC layer. The designation of element groups by Arabic numerals rather than Roman numerals is based on the Periodic Table of the Elements, which has been adopted by the American Chemical Society and is being studied for adoption by IUPAC.

It is understood that, except where specifically stated, all steps in the manufacture of electrically conductive articles according to the invention can be carried out in air at atmospheric pressure, unless otherwise indicated. Of course,
Increased rates of ambient oxygen presence and operation under pressure, used separately or in combination, are compatible with the practice of the present invention in boat fishing and can be used, although not required.

The present invention can be understood by the system diagram shown in FIG. In step A, a composition containing particles of metal-ligand compound is obtained. Each particle contains heavy pnictide, alkaline earth, and copper atoms in the same proportions as desired in the final PAC-containing conductive layer. Furthermore, these atoms are intimately mixed such that the composition of each particle is preferably essentially uniform. Volatile ligands, which can be selected from all the same or different ligands, complete the compound associated with the metal element.

The particles may be of any size convenient for coating. Although the particles can exhibit an average diameter up to the thickness of the coating being formed, more uniform films are achieved when the average particle diameter is relatively small with respect to the thickness of the film being formed. Preferably, the particles have an average diameter of less than about 2, and optimally have an average diameter of less than IJa.

The minimum average diameter of the particles is limited only by synthetic convenience.

The preferred technique of the present invention for producing metal-ligand compound particles is to dissolve the depnictide, alkaline earth, and copper metal-ligand compounds in a common solvent and then pass this solution through an atomizing nozzle into a gaseous atmosphere. It is sprayed on the surface. The solvent is selected to be vaporizable in a gaseous atmosphere.

The individual particles are thus dispersed in the gaseous atmosphere as liquid particles, resulting in completely solid particles, or particles in which the proportion of solvent is sufficiently reduced so that each of the metal-ligand compounds present is precipitated in solid form. Either way, it will stay at the collection site.

In the latter case, due to the remaining solvent no longer acting as a solvent but only as a continuous dispersed phase,
The particles form a paste. This paste constitutes a very convenient coating vehicle.

When all or substantially all initially present solvent is removed and the particles are collected in a frangible form, if desired, to promote particle adhesion, i.e. to constitute a paste. It is observed that a paste can still be formed by adding a small amount of liquid to the particles.

Only a very small amount of liquid is required to promote particle adhesion and thereby form a paste.

Typically, the liquid will constitute less than 20% of the total composition weight, preferably less than 15% of the total composition weight.

The optimum paste concentration can vary depending on the choice of method of coating the paste, but if the paste viscosity is 5X1
0' to 3 Xl06 centiboads, preferably I XI
A range of O' to 2.5 Xl06 centipoise is generally expected.

Atomization and drying are carried out in air at room temperature, although it is recognized that any gaseous medium that does not react adversely with the metal-ligand compound can be used. Furthermore, the temperature of the liquid, preferably gaseous medium forming the particles is controlled in all cases to promote the rate of evaporation of the solvent, as long as the temperature is maintained below the thermal decomposition temperature of the metal-ligand compound. can be made higher.

The advantage of reducing the metal-ligand compound by trapping it within dispersed, separate particles is that it can be used for the bulk separation of heavy pnictides, alkaline earths, and copper.
5eparation) can be prevented. This particle production approach allows individual particles produced by the method of the present invention to contain the desired proportions of heavy pnictides, alkaline earths, and elemental copper, as compared to simply evaporating the bulk solution to dryness. gives the significant advantage of This produces a solid particle coating composition that is uniform on the microscale.

In step B of the manufacturing process, metal-ligand compound particles are coated onto a substrate, preferably with a carrier liquid to form a coating paste or slurry. As shown in the figures, the resulting coated article 1 consists of a substrate 3 and a layer 5 formed by a PAC precursor (metal-ligand compound) and a film-forming solvent. Although layer 5 is shown to be coextensive with substrate 3, the particles are well suited to be deposited in any desired pattern on the substrate, especially when coated in a paste or slurry. It is recognized that For example, the paste can be deposited by any of a variety of conventional image coating techniques such as screen printing or gravure printing. Since thick conductive films are most commonly formed by screen printing techniques, the present invention is highly compatible with conventional printed circuit manufacturing methods.

In step C, article 1 is heated to a temperature sufficient to volatilize at least a portion of the ligand and carrier liquid. The resulting element 7 consists of a substrate 3 and an amorphous PAC layer 9. In its amorphous form, PAC coatings exhibit relatively low levels of electrical conductivity. As used herein, the term "amorphous" layer does not exclude some of the components that make up the layer from those that exhibit some crystallinity when observed by X-ray diffraction analysis; represents a mixture of oxides of metals. Additionally, in some instances, one or more metals,
In particular, alkaline earths exist as carbonates. However, for the purpose of this description, when referring to a mixture of oxides or an amorphous PAC layer, such carbonates are referred to under the term "
It is widely included in "oxides". It is well known to those skilled in the art that such carbonates can decompose into metal oxides upon further heating.

Once the amorphous PAC layer 9 is formed on the substrate 3,
The subsequent transformation of this intermediate layer into a final crystalline conductive PAC layer can be performed by any convenient conventional method. For example, if desired, the Has
himoto et al, Nakamoriet
The thick film crystallization method used by Al and Ho5hino et al can be used. One of the recognized manufacturing advantages of forming a crystalline conductive PAC layer as opposed to a crystalline conductive RAC layer is that the latter (the PAC layer) must be prepared in a manner such that an oxidizing atmosphere is used during its manufacture or It exhibits superconductivity, independent of whether a non-oxidizing atmosphere is used, and independent of whether it is cooled slowly at a controlled rate or rapidly.

The following disclosure is directed to a preferred approach to converting an amorphous PAC thick film into a crystalline conductive PAC thick film. Generally, conversion of the thick film to its crystalline state is achieved by heating at temperatures in the range of 750-1000<0>C.

78 when using a non-oxidizing atmosphere to convert the amorphous PAC thick film to its crystalline conductive state.
Temperatures in the range 0-850°C are preferred.

The non-oxidizing atmosphere is nitrogen or Group 18
gas, typically any convenient relatively inert gas such as argon. In addition, the non-oxidizing atmosphere burns the amorphous PAC thick film under reduced pressure,
It can be easily made by reducing oxygen availability. On the other hand, when the crystallization of the PAC layer is carried out in air or in an oxygen-enriched atmosphere, about 850-950°C
Preferably, a temperature in the range of .

A single heating step in either a non-oxidizing atmosphere or an oxygen-containing atmosphere can be used to convert an amorphous PAC thick film into a crystalline conductive PAC thick film;
Advantages have been observed that result from using a combustion process in combination with a pre-combustion process, a post-combustion process, or both. In general, optimal results with conditions achieving superconductivity at the highest possible temperature are achieved when pre-combustion, combustion, and post-combustion steps are all used in combination.

Referring to FIG. 1, process E represents the pre-combustion process, and process E
represents the combustion step and step F represents the after-combustion step.

Although crystals are observed in each of the PAC thick films 13.17 and 21, a progressively increasing desired crystallization and orientation in the crystalline phase formed is observed with the completion of each combustion.

In the presence of oxygen (e.g. in air or an oxygen atmosphere),
Preferably, the PAC layer is heated to a temperature in the range of 890-950<0>C during the combustion step E. Similar results are achieved at temperatures in the range of about 830-850°C in a non-oxidizing atmosphere. It is believed that at least some melting of the PAC composition occurs at these temperatures.

This improves adhesion to the substrate and also facilitates crystal formation and orientation, either during this step or during subsequent cooling. The PAC layer should be fired within the preferred temperature range for at least 5 minutes, preferably at least 10 minutes. Generally, the benefits of combustion can be realized quickly and long combustion times are not required. Although useful crystalline conductive PAC layers can be achieved when burn times are extended to 100 hours or more, burn times in excess of 2 hours are rarely used in practice.

In the pre-combustion step, the PAC layer is heated to a temperature lower than the combustion temperature in step E. The pre-combustion temperature ranges from 800 to 885 °C in an oxygen-containing atmosphere and 78 °C in a non-oxidizing atmosphere.
The temperature is preferably in the range of 0 to 830°C. The post-combustion temperature in step F is 870-890°C in an oxygen-containing atmosphere.
The temperature is preferably in the range of 780 to 830°C in a non-oxidizing atmosphere. Within these temperature ranges, convenient pre- and post-combustion times can be compensated for by extending the pre- or post-combustion times, generally similar to those indicated above for combustion.

, P A 0 If the crystallization of the layer is carried out in a non-oxidizing atmosphere, a somewhat lower than optimal concentration of oxygen may be present in the layer. Low-level heating of such crystalline conductive PAC layers at relatively low temperatures, e.g., temperatures down to about 480° C., in an oxidizing atmosphere, preferably oxygen, significantly increases the conductivity, e.g. To can be increased.

According to accepted percolation theory, for a layer consisting of conductive spheres placed in a surrounding non-conductive medium, for a satisfactory electrical conductivity to be achieved, the spheres are at least 45% of the layer.
It must occupy % by volume. If conductive particles of other geometric shapes, especially elongated shapes, are replaced by spheres, the conductive particles can occupy a smaller proportion of the layer volume while still achieving satisfactory layer electrical conductivity. Similarly, electrical conductivity can be achieved with a smaller proportion of electrically conductive particles when the surrounding medium is also electrically conductive. In the PAC layer of the present invention, the geometry of the conductive crystals is such that electrical conductivity is achieved when these crystals form substantially less than 45 volume percent of the layer. Satisfactory electrical conductivity is observed when the conductive crystalline phase forms only 30% by volume or less of the layer. However, it is generally preferred that the conductive crystalline phase form at least 70% by volume of the total PAC layer, optimally at least 90% by volume.

The final electrically conductive article 19 consists of a crystalline electrically conductive PAC layer 21 on the substrate 3. Through particular selection of materials and manufacturing techniques, article 19 can exhibit a high superconducting onset transition temperature.

As used herein, the term "high superconducting transition onset temperature" is defined as Tc greater than 30°C.

The method described for manufacturing electrically conductive articles with PAC layers provides several significant advantages. One of the most significant advantages is that the proportions of heavy pnictides, alkaline earths and copper elements in the KPAC layer 21 correspond exactly to the proportions present in the PAC precursor layer 5. In other words, the final proportions of rare earth, alkaline earth, and copper elements are simply determined by the desired proportions in the metal-ligand compound particles used as starting materials. This avoids the tedious and repeated trial and error adjustment of ratios required by metal oxide deposition techniques used in boat fishing, such as sputtering and vacuum deposition. Furthermore, this method does not require reducing the atmospheric pressure and therefore does not require equipment for creating high or low vacuums.

The objective is to facilitate the formation of Thus, the invention is easily applied to the manufacture of printed hybrid circuits. Patterning can be easily achieved by coating layer 5 of article 1 in the desired pattern, as described above. As an adjunct or alternative to metal-ligand compound coating patterning,
Goods? , 11, 15, or 19 PAC layer 9, 13.1
? , or 21 is patterned by conventional photoresist pattern definition and etching of the PAC layer.

Although the above method has been described for a very simple article in which the i p p, c layer is completely formed on an insulating substrate, in many practical applications only a portion of the PAC layer covers the surface of the substrate. It is recognized that it is formed directly in the For example, in the manufacture of electrical circuit components, it is common practice to first coat metal pads (conductive regions) on an insulating substrate to facilitate external lead (pin) bonding. PAC
A layer or portions of a PAC layer can be formed on an insulating substrate to provide conductive path(s) between spaced pads or other conductive regions previously formed on the substrate. Any conductive material can be precoated onto the substrate that can withstand the temperatures required to form the PAC layer. For example, gold pads are commonly used in electrical circuit component manufacturing and are fully compatible with the required PAC layer manufacturing according to the present invention. Electrical bonding to the surface of a thick film already coated and fired onto a substrate is also possible to create an electrically conductive PAC phase. Metal pads (eg, indium) can be bonded to crystalline PAC surfaces at relatively low temperatures (<200° C.). Subsequent electrical connections to the overlying metal pads can be made using conventional bonding techniques, such as soldering techniques, such as using lead-tin solder. For example, a copper wire can be soldered to an overlying pad to complete the desired electrical path.

FIG. 2 shows a cross-sectional view of an electrical circuit component 100 according to the invention. The insulating substrate 102 includes a first main surface 106 of the substrate.
and the second major surface 108 .
04 is provided. A metal pad 110 is located on the first major surface of the substrate. Thick PAC layer 114 and 1
16 are located on the first and second major surfaces of the substrate. PAC layer 114 partially overlies metal pad 110. A portion 118 of the composition forming the PAC layer extends into the aperture 104 and combines with the PAC layer on the opposite surface of the substrate. Metal leads 120 are coupled to the first PAC layer and metal lands 110 by solder 122 . A second metal lead 124 is coupled to the second PAC layer via the metal pad 112 by solder 126. Instead of soldering, the leads can also be bonded by any other convenient known means, such as ultrasonic wire bonding or thermocompression bonding.

Although the PAC layers are shown in FIG. 2 as forming linear conductive paths for simplicity, they may independently form any conductive path arrangement found in conventional circuits.

For example, the conductive path may be serpentine or undulating. Additionally, instead of forming the entire conductive path between leads 120 and 124 by itself, the PAC layer can be used to connect conventional electrical conductors such as resistors, capacitors, transistors, diodes, integrated circuit elements, and the like. Conductive paths can also be formed in series and/or in parallel with circuit components.

Any heavy pnictide mixed alkaline earth copper oxide composition known to be convertible to a conductive crystalline phase can be used in forming the coated articles of the present invention. The term "heavypnictide mixed alkaline earth copper oxide" means a composition of matter containing at least one heavy pnictide element, at least two alkaline earth elements, copper, and oxygen. The term "depnictide" refers to elements of Group 15 having an atomic number of at least 51, i.e.
Used to specify bismuth and antimony, alone or in combination with small amounts of lead. Generally, depnictide is bismuth alone or bismuth and 0 to 3
0 mol% of antimony or lead or a combination of antimony and lead. The term "alkaline earth" refers to Group 2 elements. In a preferred embodiment, the mixed alkaline earth element is a combination of calcium and at least one heavy alkaline earth, ie, an alkaline earth having an atomic number of at least 38.

The preferred heavy alkaline earth is strontium alone or in combination with strontium and 0 to 10 mol% barium, based on the total alkaline earth.

Superconductivity is a metal ratio: P2Ax-yCayCu.

(wherein P is a heavy pnictide consisting essentially of bismuth and 0 to 30 mol % of one of antimony or lead or a combination of antimony and lead; A is essentially strontium and 0 to 10 mol % of antimony or lead; % barium, X is an integer 3 or 4, y ranges from 0.5 to 2, and 2 is an integer 2.
or 3) is observed in the crystal phase of heavy pnictide mixed alkaline earth copper oxides.

In preferred embodiments where the heavy pnictide is bismuth and the heavy alkaline earth is strontium, the superconducting oxide phase has a metal ratio: B 12 S r w-y Ca y Cus (wherein
x, y and 2 are as described above). Studies of bulk bismuth strontium calcium copper oxide (BSCCO) relate the following crystalline phases to its superconductivity.

B5CC0-211124 people 8″KBSCC
O-221230 people 80'KBSCCO-22
2337 people 105'K (in the table, 4 Arabic numerals indicate the ratio of metal atoms in the crystal, angstroms indicate the identified crystal unit cell C-axis length, and temperature indicates TO).

Strontium and calcium are these escc.

Although shown as integers in the composition, strontium and calcium can be interchanged in all ratios within the limits of y suggesting that they form a solid solution. Thus, the escco crystalline phase exhibiting superconductivity above the boiling point of liquid nitrogen (77''K), preferably present in the thick film of the electrically conductive element of the present invention, has the following relationship: B izs ra-, Ca , Cu2 (wherein y ranges from 0.5 to 1.5), and B
i2 S r 4-yCa, Cu3 (wherein y is 1.
5 to 2.0).

To form these superconducting phases as thick films, the same metals in the same proportions are preferably used in selecting the metal-ligand compounds used as starting materials. However, it is not essential that the metal forming the metal-ligand compound starting material be coated in the same proportion as that found in the superconducting crystalline phase(s) of the final thick film.

During crystallization, the excess metal or metals are simply excluded from the superconducting phase(s) formed.

The excluded metals remain as a separate phase in the final thick film coating. As shown in the examples below, large imbalances in metal proportions are perfectly compatible with making superconducting thick films.

The metal-ligand compound has the following relationship: P a A b-c C a c Cu d (where P is essentially bismuth and 0 to 30 mol% antimony or lead-1 or a combination of antimony and lead). A is a heavy alkaline earth consisting essentially of strontium and 0 to 10 mol% barium, a ranges from 2 to 5, and b ranges from 3 to 4. range, C ranges from 0.5 to 2, and d ranges from 2 to 5
It is preferable that the selection is made so as to satisfy the following.

When the heavy pnictide is bismuth and the heavy alkaline earth is strontium, the preferred ratio of metals in the metal-ligand starting material is according to the following relationship: B lll5 rb-
ecaccud (wherein a ranges from 2 to 5, b ranges from 3 to 4, C ranges from 0.5 to 2, and d ranges from 2 to 5
) satisfies the following. When the metal-ligand starting material contains excess of either bismuth or copper, B5CC0-2
223 superconducting crystalline phase is particularly preferred.

The ligands present in the metal-ligand compound do not form part of the final article and can therefore be selected solely on the basis of convenience in carrying out the steps of the method. The ligand is first selected for its ability to form a solution in which the depnictide, alkaline earth, and copper in combination with the ligand are each soluble in the desired proportions. Second, the ligand is selected to be volatile during heating to form the intermediate PAC layer.

The term "volatile" means that the ligand or its constituent elements other than oxygen can be removed from the substrate surface at temperatures below the crystallization temperature of the PAC layer.

Inorganic-ligands such as nitrate, sulfate, and halide ligands are representative of preferred ligands that meet the above criteria. Particularly preferred are nitrates, bromides, and chlorides. Generally, the ligands are selected such that each of the depnictide, alkaline earth, and copper ligand compounds exhibits roughly similar solubility properties.

Any vaporizable solvent for metal-ligand compounds can be used for particle preparation. Also, this solvent does not form part of the final article. Polar solvents such as water or alcohols (eg, methanol, ethanol, propatool, etc.) are particularly suitable for use with metal-ligand compounds, including the inorganic ligands described above.

When the paste is coated, it contains either a small residual portion of the original solvent for the metal-ligand compound or a different liquid to promote bonding. The liquid part of the paste must be volatile. All of the above vaporizable solvents meet this criterion.

The paste, except for the metal-ligand particles, may have the same composition as known inks used in screen printing. Screen printing inks typically include an active ingredient (supplied in the present example by metal-ligand particles), a binder to promote substrate adhesion (e.g., a glass frit or a crystalline oxide powder), and the rheological properties of the ink. The screening agent used to enhance the oxidation rate typically includes a high molecular weight polymer such as poly(vinyl alcohol) or poly(ethylene glycol) and a liquid (most commonly water or alcohol). Metal-based printing without the need to include other screen printing ink components
It is a particular advantage of the present invention that the ligand particles and liquid together provide excellent rheological and adhesive properties.

Thick films produced according to the invention can vary in thickness within a wide range. Final thickness is approximately 5-200
- is contemplated, with thicknesses of about 10 to 100 ja for thickest film applications.

Larger coating thicknesses are possible with care to avoid thermal stresses. Thin PAC films can be easily produced by the method of the present invention.

The substrate of the thick film element of the present invention is insulating simply because it is insulating compared to the electrical conductivity of the PAC layer. As used herein, the term "insulating substrate" refers to a substrate in which current flow is greater than that of the substrate on which the PAC layer is formed.
It refers to any substrate that has an electrical resistance of a value significantly greater than the electrical resistance of the PAC layer that passes predominantly through the layer. When the circuit element is intended to be used at temperatures well below ambient temperature, such as the Tc or To of the PAC layer, the insulating substrate will actually become more conductive than the PAC layer at ambient temperature.

Electrically conductive crystalline PAC layers can be formed on a wide variety of substrates. Generally, any known electrically conductive substrate that can withstand the processing temperatures can be used. for example,
All metals, glasses, ceramics and semiconductor substrates are
Crystalline P applied by one or more of the above methods
It has sufficient thermal stability to accommodate the AC layer. Both polycrystalline and single crystalline substrates have been successfully used.

The present invention creates PAC thick films that initially exhibit high Tc and superconductivity when coated onto a substrate consisting of aluminum oxide or aluminum nitride.

Thick film PAC layers of the present invention can be formed on both single crystal and polycrystalline alumina. Additionally, substrates containing aluminum and oxygen in combination with one or more metals are contemplated, such as in spinel substrates. M
gAl2O, is an exemplary substrate of this type. Of course, 1
It is to be appreciated that spinels, in addition to those containing aluminum as the species or more metallic element, can be used as substrates useful in the practice of this invention.

Any of the various other types of substrates known to be useful in forming PAC thin or thick film conductive elements can also be used.

Alkaline earth oxides constitute a preferred type of substrate material. These I-O's are relatively inert refractory materials that exhibit limited interaction with the PAC layer during their formation. Magnesia in single crystal (ie, periclase) or polycrystalline form constitutes a particularly preferred substrate material because of its low level of interaction with the PAC layer. Strontium titanate constitutes another preferred alkaline earth oxide substrate material because it can be easily formed into perovskite crystalline forms.

Semiconductor wafers, particularly single crystal silicon and ■-■ compound wafers, also constitute useful types of substrates for the articles of this invention.

Another specially contemplated class of substrate materials are refractory metals. Of course, such metals are well suited to withstand PAC layer crystallization temperatures of 1000° C. or higher.

Refractory metals such as tungsten, tantalum, titanium, and zirconium are particularly contemplated. The refractory metal can form a refractory layer over which the entire substrate or PAC layer is coated.

Although it is believed that some interaction between the substrate material and the adjacent PAC layer occurs when the article is heated above about 900°C, thick film PAC layers may It is much less affected than the PAC or RAC layers. Thus, direct coating of PAC thick films onto various substrate materials is contemplated.

If the barrier layer is intended to further reduce or eliminate the interaction between the substrate and the PAC thick film,
Barriers can be selected from a variety of materials. The refractory metals mentioned above, platinum group (platinum, osmium, or iridium) metals, gold, and silver are all viable barrier materials.

Under processing conditions the refractory metals convert to the corresponding oxides. When the substrate is silicon, a metal silicide barrier layer can be used. Aluminum nitride and silicon nitride are both contemplated barrier layer materials. Generally, any of the preferred substrate compositions described above also form useful barrier layer compositions. Of course, the selection of a particular barrier layer or barrier layer combination will, in many instances, be influenced by the composition of the substrate and the opportunity to simplify the manner in which particular substrate and barrier layer selections are made.

A particularly preferred barrier layer triad arrangement specifically intended for silicon substrates is a first triad layer located adjacent to the silicon substrate consisting essentially of silica, consisting essentially of at least one Group 4 (Group
4) A third triad layer consisting of a heavy metal (i.e. zirconium or hafnium) oxide and removed from the silicon substrate, consisting essentially of silica and at least one Group 4
4) Consists of a nitriat layer consisting of a mixture with a metal oxide. This barrier layer protects the silicon substrate from contamination by the overlying conductive layer, in particular against copper contamination, and protects the conductive layer from silicon contamination.

The first step in the method for forming such a barrier layer triad is to form a silica layer on a silicon substrate to a thickness of at least 2000 nm. The silica layer is preferably at least 5000 Å thick. Any convenient thickness of silica layer can be formed beyond the required minimum thickness. Formation of the silica layer on the silicon substrate can be accomplished by any convenient known means and does not form part of the present invention. Silica layers are conveniently formed in many instances by oxidation of the surface of a silicon substrate to form a grown silicon oxide layer. Also, a silica layer can be deposited.

Following the formation of the silica layer, at least one group 4 (Gr)
oup4) Heavy metals are deposited on top of the silica layer.

The term "Group 4 heavy metal" is used herein to refer to Group 4 heavy metals of the Periodic Table of the Elements as adopted by the American Chemical Society.
p4) is used to indicate the elements zirconium and hafnium. Group 4 elements also refer to Group rVA elements using IUPAC nomenclature for the Periodic Table of the Elements. The Group 4 heavy metal(s) are deposited to form a layer that is approximately 1000 to 5000 nm thick. At smaller layer thicknesses, the barrier effectiveness is reduced due to insufficient group 4 heavy metals, while at larger layer thicknesses the physical stress within the layer increases, which results in physical defects. The Group 4 heavy metal layer can be deposited onto the silica layer by any convenient known technique adapted to achieve the desired layer thickness. Techniques such as vacuum deposition, chemical vapor deposition, metal organic deposition and sputtering are suitable to achieve the desired layer arrangement.

The next step is to convert the silica and group 4 heavy metal layer into a barrier layer triad. The first step to achieve this goal is to heat the two initially formed layers to a temperature at which oxygen migration occurs in the absence of a reactive atmosphere. Heating is best done in vacuum or in an inert gas atmosphere, such as an argon atmosphere. The purpose of this is to move oxygen from the silica layer into the Group 4 heavy metal layer. This forms a Group 4 metal oxide within the Group 4 heavy metal layer at a location remote from the underlying silica layer. At the same time, the group 4 heavy metal reacts with the silica layer to form a group 4 heavy metal silicide at the interface.

As a result, a first triad layer consisting essentially of silica, a third triad layer consisting essentially of at least one Group 4 heavy metal oxide, and a first triad layer consisting essentially of at least one Group 4 heavy metal silicide. A barrier layer triad is formed consisting of a first nitriat layer of a barrier triad interposed between a first nitriatide layer and a third triad layer.

The time and temperature of heating required to effect the necessary oxygen transfer are interrelated. Oxygen transfer is achieved with lower temperatures and longer heating times, or higher temperatures and shorter heating times.

Generally, temperatures of at least 700° C. are required for meaningful oxygen transfer to occur, even when heating times are as long as 2 hours or more. On the other hand, it is not intended to use heating temperatures above about 1200°C. Approximately 750
It is preferred to use a heating temperature in the range -1000<0>C, with the optimum heating temperature being within the range of about 800-900<0>C. Adequate oxygen transfer can be achieved by rapid heat annealing near maximum temperature for times as short as about 1 minute, but generally preferred heating times are about 30 to 60 minutes.

Although the first nitriat layer is initially formed from a Group 4 heavy metal silicide, this layer in the final conductive element is converted, in whole or in part, to a mixture of silica and Group 4 heavy metal oxide. This conversion results from subsequent heating in the presence of oxygen, such as is used to form a conductive crystalline PAC layer formed over the barrier triad.

From the foregoing it can be seen that the silicon substrate and the barrier layer triad together form the following sequence:

Third Triad Layer Second Triad Layer Third Triad Layer Silicon Substrate In the completed conductive element of the present invention, the first triad has a thickness of at least about 1000 nm. The maximum thickness of this layer is not critical and may range from 1 to more if desired. The second and third barrier triad layers also each preferably have a thickness of at least about 1000 Å, but typically each has a thickness of 5000 Å or less.

〔Example〕

The following examples demonstrate the practice of the invention. The nitric acid described in the examples was fuming nitric acid in all examples.

All steps were performed in air except where noted.

Example 1 This example demonstrates the formation of a conductive thick film crystalline coating of bismuth strontium calcium copper oxide (BSCCO) on a polycrystalline alumina substrate.

A FS-1 particle forming solution was prepared by mixing the following components in the following ratios.

Bi (NO3) 351420
48.51 gSr (NO3) 2
21.16 g(:a (NO3) 24H2
08,21gCu (NO3) 22.5L0
23゜27g820
300,00mLHNOs
20.00mL.

The water used was distilled water. First, bismuth was dissolved in water and nitric acid. Other nitrates were then added to give a clear paleocoloured solution. The original objective was to prepare a composition containing bismuth, strontium, calcium, and copper in an atomic ratio of 2212, but an inductively coupled plug? (
ICP) analysis (inductively coupled
Chemical analysis by plasma analysis showed that it had a 3313 ratio composition. A possible explanation is that the calcium nitrate contained more water than the stated amount. PF5-1 was diluted in 1 liter of water and 15 mL of nitric acid added to avoid precipitation.

PF5-1 was converted to a powder by spray drying. Yamat
An oT14 model GA-31 spray dryer was used in its standard mode of operation.

Inlet temperature 200℃ Outlet temperature 90℃ Pump set 2.0 Dry air 0.29-0.35m”7 minute atomization air 0.29MPa #2050S
A #64-5SS air nozzle and a #64-5SS liquid nozzle were used.

Preheat the spray dryer for 1 hour before spraying PF5-1,
A temperature of approximately 80° C. was maintained during the run.

A paste was formed from the powder obtained by spraying by adding 19% water by weight based on the weight of the powder. It was clear that this paste had excellent rheological properties for screen printing. This paste was coated onto a 99.5% pure polycrystalline alumina substrate and heated under oxygen on a hot plate at a rate of 3°C/min to a temperature of about 400°C.

The coated substrate was placed in an oven preheated to 875°C and heated for 10
It was maintained for a minute. Examination of the thick film structure revealed two different types of regions. Long needle-like crystals were observed in the first type of region, and a resistance greater than 100 ohms was observed in this type of region. Dense mats of crystals appeared in the second type of area, and resistances of 20-60 ohms were observed in this type of area.

Example 2 This example shows 30 people (escco-
2212) Demonstrates the preparation of crystalline thick films.

Aqueous stock solutions of 0.1 molar bismuth nitrate, strontium nitrate, and copper nitrate were prepared. Additional nitric acid was added to the bismuth solution (7.5 mL) to completely dissolve the powder.
/LH,0). Additionally, a 0.05 molar calcium nitrate solution was prepared. Equal parts of these solutions were mixed to prepare the final nitrate solution used for spray drying. The following parameters were used.

Population temperature 200℃ Outlet temperature 80℃ Pump settings 2.0 Dry air 0.32m’/min.

Atomizing air 0.2 MPa #2050SS liquid nozzle and #64-5SS air nozzle were used. After about 1 hour, stop spraying and then 0.25
Restarted with atomizing air pressure increased to MPa. The outlet temperature dropped to 60°C, but then returned to 80°C. The solution was sprayed at a rate of approximately 400 mL/hr. big nozzle (
After changing to #70ss air, #2850SS liquid), the outlet temperature was reduced to 50° C. and the solution passed through the system without completely drying. To maintain salt solubility, 20 mL of nitric acid was added to the solution and the solution was heated to about 80°C. The final solute concentration of the solution is 0.03
g/mL, and a usable amount of powder was produced.

A paste was prepared from the powder by adding 20% by weight neat water based on the weight of the powder. The atomic ratio of bismuth, strontium, calcium and copper in the paste was 2212. Hereinafter, this paste will be referred to as 2212 paste.

The 2212 paste was coated onto a 99°5% pure polycrystalline alumina substrate and heated at a rate of 3°C/min to 500°C, held at 500°C for 5 minutes, and heated at a rate of 5°C/min to 880°C. and held at 880°C for 20 minutes, and then cooled to room temperature at less than 20°C/min.

Although the thick film adhered well to the substrate, the structure was not uniform. In the first type of region, the thick film consisted mainly of needle-like crystals. The second type of region consisted primarily of small particles with a small number of large platelets. X-ray diffraction analysis of the second type of region showed very little 24A phase and mainly randomly oriented 30A phase. The sheet resistance of the second type region was 24 Ω/hole.

Example 3 This example shows a superconducting crystal B5C on a polycrystalline alumina substrate.
A C0-2212 thick film is shown.

To increase the solubility of bismuth nitrate, add nitric acid (20 m
L/LH20) was mixed with the starting material of Example 2.

The spray drying parameters used to convert the fresh solution to paste were as follows.

Population temperature 200℃ Outlet temperature 80℃ Aspirator settings 3 Pump settings 2.0 Dry air 0.230.27m’/min.

Atomizing air 0.29 MPa #2850SS liquid nozzle and #70SS nozzle were used.

2212 paste was prepared from powder by adding water. This paste was coated onto the (100) crystal surface of several single crystal magnesia substrates.

The coated substrate was heated to 500°C at a rate of 3°C/min.
Hold at 0°C for 5 minutes, heat to 880°C at a rate of 5°C/min, hold at 880°C for 20 minutes, and then heat at 20°C/min.
Cooled to room temperature at a rate of less than a minute.

The 2212 paste was coated onto a 99.5% pure polycrystalline alumina substrate. The sample was heated to a temperature of 8°C at a rate of 5°C/min.
heated to 00°C and held at 800°C for 30 minutes,
It was then cooled to room temperature at a rate of less than 20°C/min. The samples were loaded into a furnace preheated to 900°C and held for 7 minutes before being rapidly cooled to room temperature.

X-ray diffraction analysis showed randomly oriented 30A phase crystals and other second order phases.

The sample was then placed into a furnace preheated to 875°C,
and held for 10 minutes before quenching. X-ray diffraction analysis was not significantly different.

The sample was again placed into the furnace preheated to 900°C, held for 12 minutes, and then rapidly cooled to room temperature.

X-ray diffraction analysis showed a very well oriented 24A phase and a small amount of 3OA phase.

The sample was placed in a furnace preheated to 880°C, held for 12 minutes, and then rapidly cooled to room temperature. Very well oriented 30A phase and very small amount of 24A by X-ray diffraction analysis
phase and other second-order class phases were shown.

Tc was ±1χ at 87', and To was ±1'' at 62'.

Example 4 Superconducting thick films can also be formed on the surface of an aluminum nitride support using techniques similar to those described above.

〔Effect of the invention〕

In accordance with the present invention, electrically conductive thick (at least 5-channel) films of superconducting crystalline pnictide alkaline earth copper mixed oxides can be formed on alumina and aluminum nitride supports.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the method steps and the article produced thereby. FIG. 2 is a cross-sectional view of the electric circuit component. DESCRIPTION OF SYMBOLS 1... Article, 3... Substrate 5... Layer, 7... Article, 9... Layer,
11... Goods, 13... Thick film,
15... Goods, 17... Thick film, 19.
...Goods, 21...Thick film, 100...
Circuit component, 102... Insulating substrate, 104... Aperture, 106... First main surface, 108...
Second main surface, 110... Metal pad, 112... Metal pad, 114... PAC layer, 116...
PAC layer, 118... Part of PAC composition, 120... Metal lead, 122... Solder, 12
4...Metal lead, 126...Solder. Procedural amendment (method) Display of the case 1999 Patent Application No. 338825 Name of the invention Person who makes amendments to superconducting thick film for hybrid circuit components Relationship to the case Patent applicant 6, Specification subject to amendment 7, Amendment An engraving of the detailed statement of contents (no changes to the contents) 8. One engraving of the list of attached documents

Claims (1)

[Claims] 1. A circuit element comprising an electrically conductive film having a thickness of at least 5 μm comprising a superconducting crystalline heavy pnictide alkaline earth copper mixed oxide and a substrate, characterized in that the substrate is aluminum oxide or aluminum nitride. circuit elements.